<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a{
            width: 1200px;
            height: 100px;
            background-color: #f00;


            /* 百分比   椭圆 >= 50% */
            /* border-radius: 90%; */


            /* 超过高度的一半 */
            /* border-radius: 50px; */

            /* css3的属性 */
            border-radius: 10px 20px 30px 40px;
        }
    </style>
</head>
<body>

    <div class="a"></div>
    
</body>
</html>